Add option to format x ticks as times

src/main.c

@@ -3,6 +3,7 @@
 #include <fcntl.h>
 #include <gtk/gtk.h>
 #include <pango/pangocairo.h>
+#include <time.h>
 
 /* TYPES!!! */
 
@@ -56,6 +57,7 @@ struct context {
 
 	PangoFontDescription* label_font_description;
 	char* xlab;
+	bool time;
 	PangoLayout* xlab_layout;
 	char* yllab;
 	PangoLayout* yllab_layout;
@@ -221,6 +223,13 @@ int main( int argc, char** argv ) {
 			.arg_data = &( context->yrlab ),
 			.description = "Right y-axis label",
 			.arg_description = "label",
+		}, {
+			.long_name = "time",
+			.short_name = 'T',
+			.flags = G_OPTION_FLAG_IN_MAIN,
+			.arg = G_OPTION_ARG_NONE,
+			.arg_data = &( context->time ),
+			.description = "Format x-axis as time",
 		}, {
 			NULL,
 		},
@@ -960,8 +969,7 @@ static void plot_draw( GtkDrawingArea* plot,
 	bool rset = false;
 
 	for ( struct data* data = context->data;
-			NULL != data;
-			data = data->next ) {
+			NULL != data; data = data->next ) {
 
 		xrange[1] = data->x;
 
@@ -1086,8 +1094,16 @@ static void plot_draw( GtkDrawingArea* plot,
 				context->xtick_layouts.layouts[i],
 				context->tick_font_description );
 		}
+		if ( context->time ) {
+			time_t t = xrange[0] + ( (double) i ) / ( xdivs - 1 ) *
+				( xrange[1] - xrange[0] );
+			struct tm* tm = gmtime( &t );
+			strftime( tick_buffer, 512, "%H:%M:%S", tm );
+		} else {
 			sprintf( tick_buffer, "%.3g",
-			xrange[0] + ( (double) i ) / ( xdivs - 1 ) * ( xrange[1] - xrange[0] ) );
+				xrange[0] + ( (double) i ) / ( xdivs - 1 ) *
+					( xrange[1] - xrange[0] ) );
+		}
 		pango_layout_set_text(
 			context->xtick_layouts.layouts[i], tick_buffer, -1 );
 		int tick_size;